TY - JOUR
T1 - Delineating the mode of action of adenosine A<sub>1</sub> receptor allosteric modulators
JF - Molecular Pharmacology
JO - Mol Pharmacol
M3 - 10.1124/mol.110.064568
AU - Valant, Celine
AU - Aurelio, Luigi
AU - Urmaliya, Vijay B.
AU - White, Paul
AU - Scammells, Peter J.
AU - Sexton, Patrick M.
AU - Christopoulos, Arthur
Y1 - 2010/06/14
UR - http://molpharm.aspetjournals.org/content/early/2010/06/14/mol.110.064568.abstract
N2 - Despite the identification of 2-amino-3-benzoylthiophenes (2A3BTs) as the first example of small molecule allosteric potentiators of agonist function at a G protein-coupled receptor (GPCR) -- the adenosine A1 receptor -- their mechanism of action is still not fully understood. We now report the mechanistic basis for the complex behaviors noted for 2A3BTs at A1 receptors. Using a combination of membrane-based and intact-cell radioligand binding, multiple signaling assays, and a native tissue bioassay, we found that the allosteric interaction between 2A3BTs and the agonists, 2-Chloro-N6-[3H]cyclopentyladenosine ([3H]CCPA) or (-)-N6-(2-Phenylisopropyl)adenosine (R-PIA), or the antagonist, [3H]8-Cyclopentyl-1,3-dipropylxanthine ([3H]DPCPX), is consistent with a ternary complex model involving recognition of a single extracellular allosteric site. However, when allowed access to the intracellular milieu, 2A3BTs have a secondary action as direct G protein inhibitors; this latter property is receptor-independent as it is observed in non-transfected cells and also after stimulation of another GPCR. In addition, we found that 2A3BTs can signal as allosteric agonists in their own right but show bias towards certain pathways relative to the orthosteric agonist, R-PIA. These results indicate that 2A3BTs have a dual mode of action when interacting with the A1 receptor and that they can engender novel functional selectivity in A1 signaling. These mechanisms need to be factored into allosteric ligand structure-activity studies.The American Society for Pharmacology and Experimental Therapeutics
ER -